In the instruments here contemplated, the oscillations of the several tone generators thereof are picked up by associated electroacoustic transducers converting them into electric audio signals. These transducers may operate inductively, capacitively or piezoelectrically, for example; they may also be constituted by strain gauges on a string-supporting bridge as described in my prior U.S. Pat. Nos. 4,228,715 and 4,292,875. The transducers are provided with output circuitry for acoustically reproducing the oscillations of the corresponding tone generators, usually through a loudspeaker, after suitable amplification. That output circuitry may further include certain components, such as dynamic-range compressors and sustainers, for electronically controlling the period during which an audio signal persists beyond the instant of excitation of the associated tone generator and for establishing a selected fade-out rate during that period; circuitry of that kind is known primarily from electronic music synthesizers, e.g. as described in U.S. Pat. No. 4,336,734 and others referred to therein.
The aforedescribed components of electronic synthesizers, however, do not operate satisfactorily in electroacoustic instruments designed to produce natural-sounding tones in the fade-out phase. The length of the fade-out period is limited by the extent to which the generated audio signal can be amplified within an acceptable signal-to-noise ratio. When the noise becomes excessive, the amplification must be instantly terminated so as to cut off the sound. This is inconsistent with natural tone perception.